Mechanisms and circuits for facsimile reproducing systems

ABSTRACT

A cylindrically shaped copy sheet is rocked forward and back during and synchronously with the first and second, respectively, of two consecutive revolutions of a drum carrying film sheets. During the forward rocking, the copy sheet is line scanned and tone values detected by such scanning are converted into intensity modulations of light beams produced by glow lamps and scanning the film sheets to expose color separations thereon of the original. During the second revolution, the glow lamps are extinguished by transistorized circuits providing a firing voltage pulse for re-starting the lamps. Also during the second revolution, the copy sheet and film sheet are each moved an axial step to permit generation of congruent raster scanning patterns over all sheets. Means are provided to adjust the enlargement ratio. The copy sheet is bent into cylindrical shape by pressing it against a template surface such that part of the sheet is backed by the surface and part projects into the scanning light beam therefor. The sheet is axially displaced relative to such beam by sliding the sheet over such surface.

United States Patent Barkman et al.

[451 July 18,1972

[54] MECHANISMS AND CIRCUITS FOR FACSIMILE REPRODUCING SYSTEMS [7 2] lnventors: Byron L. Barkman, Milford; William West Moe, Stratford; Austin Ross, Monroe, all of Conn.

Printing Developments, Inc., New York, NY.

[22] Filed: Aug. 31, 1970 [21] Appl. No.: 68,169

Related U.S. Appllcatlon Data [73] Assignee:

' [62] Division of Ser. No. 698,255, Jan. 16 1968, Pat. No.

- [56] References Cited UNITED STATES PATENTS Pfleger ..l78/6.7 R Andersen. .....340/339 X Colton ..340/324 R 2,535,610 12/1950 Thompson ..178/6.7R 3,146,436 8/1964 Crow ..340/324R Primary Examiner-Howard W. Britton v Attorney-Brambaugh, Graves, Donohue & Raymond [57]- ABSTRACT A cylindrically shaped copy sheet is rocked forward and back during and synchronously with the first and second, respectively, of 'two consecutive revolutions of a drum carrying film sheets. During the forward rocking, the copy sheet is line scanned and tone values detected by such scanning are converted into intensity modulations of light beams produced by glow lamps and scanning the film sheets to expose color separations thereon of the original. During the second revolution, the glow lamps are extinguished by transistorized circuits providinga firing voltage pulse for re-starting the lamps. Also during the second revolution, the copy sheet and film sheet are each moved an axial step to pemiit generation of congruent raster scanning patterns over all sheets. Means are provided to adjust the enlargement ratio.

The copy sheet is bent into cylindrical shape by pressing it against a template surface such that part of the sheet is backed by the surface and part projects into the scanning light beam therefor. The sheet is axially displaced relative to such beam by sliding the sheet over such surface.

4 Claim, 7 Drawing Figures Patented July 18, 1972 I 3,678,187

4 'Sheets sheet :3

I NVEN'TORS BYRON BARKMAN, WILLIAM WEST MOE a AUSTIN Ross WWM ATTORNEYS Patented July 18,1972 3,678,187

4 Sheets-Sheet 5 INVENTORS BYRON L. BARKMAN, WILLIAM WEST MOE a AUSTIN ROSS Arromvsrs Patented July18, 1972 Y v 3,678,187

4 Sheets-Sheet 4 IMAGE SIGNAL PROCESSING UNIT 42 g6; SKIP SCAN CONTROL AND FROM GLOW LAMP STARTING CIRCUITS MICROSWITCH BYRON L. BARKMAN, WILLlAM WEST MOE a ATTORNEYS MECHANISMS AND CIRCUITS FOR FACSIMILE REPRODUCING SYSTEMS This is a divisional application of Ser. No. 698,255 filed Jan. 16, 1968, now US. Pat. No. 3,558,813.

This invention relates generally to facsimile reproducing systems in which first and second beams of light scan synchronously over, respectively, a copy sheet and a sensitized photographic film sheet, and in which tonal values detected by scanning of the copy sheet are converted into a signal controlling the intensity of the second beam to produce exposure on the film sheet of an-image derived from the copy sheet. More particularly, this invention relates to improvements in facsimile reproducing systems similar to that disclosed in US. Pat. No. 3,109,888 issued Nov. 5, 1963 in the name of W. W. Moe.

In the system of the mentioned Moe patent, a copy sheet in the form of a color transparency is stretched between opposite arcuate sides of a frame to conform to a cylindrical surface intercepting the path of a stationery scanning beam and having an axis normal to and intersecting the axis of that path. A single line of scanning of the sheet by the beam is produced by rocking the frame about the axis of the cylindrical surface through a fixed angle from a reference angular position. The sheet is then returned to reference position by a rearward rocking motion not used for scanning purposes. Between each line scanning of the sheet by the beam, the frame is displaced one step in the direction of the axis of the cylindrical surface so as to cause successive line scans over the copy sheet to form a raster scanning pattern therefor.

The scanning beam is modulated in color and intensity by the tone values of the color transparency through which the beam passes in the courseof scanning. The modulated beam is converted into different color component electric signals controlling the currents through respectively corresponding glow lamps to thereby control the intensities of respectively corresponding exposing light beams emitted by those glow lamps. Each of -the exposing light beams is projected to a separate zone of a drum which undergoes rotary motion and stepwise axial motion relative to the exposing beams in synchronism with, respectively, the rocking motion and the axial stepwise motion of the frame. The exposing beams are thus caused to scan in raster patterns over sensitized photographic film sheets mounted on the drum to those zones, the different beams exposing different color separation images of the original color transparency on the different film sheets.

, The system of the Moe patent has the disadvantage that,

whenthe copy sheet is large, it becomes difficult to stretch the sheet within its frame so as to conform the sheet with desired accuracy to the ideal geometric cylindrical surface.

Because, in the system of the Moe patent, there is one complete forward and back motion of the frame and copy sheet during each revolution of the mentioned drum, the film sheets must occupy less than half the drum circumference in order to permit the return motion of the frame to occur when the exposing light beams are falling on a blank area of the drum. Otherwise, those beams would expose a false image on the film sheets in response to illumination of the copy sheet during the return motion of the frame. The requirement, however, that the film sheets not occupy more than half the drum circumference is disadvantageous because half of the circumference of the drum is thereby wasted.

It is accordingly an object of this invention to provide facsimile reproducing systems of the sort described in which copy sheets of large sizes (as well as small sizes) are made to conform with good accuracy to an ideal cylindrical surface.

A further object of this invention is, in connection with a system of such type, to provide improvements which permit the film sheet to occupy more than half the drum circumference and/or which permit adjustment of the ratio between the size of the scanned area of the copy sheet and the size of the scanned areas of the one or more film sheets.

Still another object of this invention is to provide circuitry ,for restarting a glow lamp after it has been extinguished.

For a better understanding of how these and other objects of the invention are realized, reference is made to the following descriptions of an exemplary embodiment thereof, and to the accompanying drawings wherein:

FIG. 1 is a plan view of the motioned embodiment with a portion of the embodiment being broken away to simplify the drawing;

' FIG. 2 is an enlarged plan view of a portion of the FIG. 1 embodiment;

FIG. 3 is a front elevation (taken as indicated by the arrows 3-3 in FIG. 2) of the portion shown in F IG. 2;

. FIG. 4 is a side elevation (taken as indicated by the arrows 4-4 in FIG. 1) of the embodiment of FIG. 1;

FIG. 5 is a side elevation in cross section (taken as indicated by the arrows 5-5 in FIG. 1) of the embodiment of FIG. 1;

FIG. 6 is a plan view of the portion of the FIG. I embodiment which involves the drum, the glow lamps and the circuits for those glow lamps, and which is the portion broken away in FIG. I; and

FIG. 7 is a schematic diagram of one of the circuits shown in FIG. 6. 1

STRUCTURE Referring now to FIG. 1, a bed 10 supports an electric motor 11 driving at constant rotary speed a shaft I2 journaled along its length in bearing 13 and having its rightward end connected to a 2:1 gearbox l5. Mounted on shaft 12 to rotate therewith is a drum 16 carrying four axially spaced sensitized photographic film sheets 17 20 (see FIG. 6) of which only the sheet 17 is shown in FIG. 1. Each of the sheets 17 20 extends around the drum 16 to occupy more than half its circumference.

Disposed to one side of the drum 16 is a projector carriage movable on ways 24 parallel to the axis of the drum. Carriage 25 supports four projectors 27 (FIG. 6) of .which each is comprised of a glow lamp 26 and optical means for forming the light emitted by thatlamp into an exposing light beam. The respective light beams from the projectors 27 30 are directed to the separate axial zones of drum 16 at which the film sheets 17 20 are mounted on the drum. As that drum rotates, carriage 25 is moved axially rightward one incremental step during the second revolution in each non-overlapping pair of consecutive revolutions of the drum. That stepwise axial movement of the carriage is effected by apparatus 31 which may be, say, driven by motor 11 (as indicated by the dash line 32 in FIG. 1), and which may be similar to the indexing apparatus disclosed in US Pat. No. 3,288,925 issued on Nov. 29, 1966 in the name of W. W. Moe.

The glow lamps of the projectors 27 30 are connected (FIG. 6) through skip-scan circuits 35 (later described in more detail) and through respective cables 37 40 to a unit 41- which effects electronic color processing of different color component image signals supplied thereto by a cable 42. Unit 41 may be a color signal processing system similar to those disclosed in US. Pat. No. 2,873,312 issued Feb. 10, 1959 in the name of W. W. Moe or US. Pat. No. 3,194,883 issued July 13, 1965 in the name of Austin Ross. What unit 41 does is, briefly, to (a) receive three separate electrical signals representative of the blue, green and red color components of scanned tone values of a colored original image, (b) subject those input signals to tone range compression, color correction masking, under color removal and other processing, (c)-utilize such processing to supply yellow, magenta", cyan" and black" signals to, respectively, the projectors 27, 28, 29 and 30 to cause the light beams from mgidti'iam' s of those projectors to expose yellow, magenta, cyan and black separation images of the colored original on, respectively, the films l7, l8, l9 and 20.

The input signals for unit 41 are derived in a manner as follows.

The rotary motion of shaft 12 (FIG. I) is reduced 2:1 in gearbox l5 and is then transmitted to a shaft 45 journaled in bearing 46 mounted on bed 10. It will be evident that shaft 45 undergoes one full revolution for each two full revolutions of shaft 12.

Shaft 45 has fixedly mounted on its right-hand end a main cam 47 and an auxiliary cam 48. The camming face of cam 47 -is engaged by a cam follower roller 49 (FIG. 4) mounted on along the length of the slot.

Set screw device 57 serves as a pivot connection for the lower end of a drive rod 60 of which the upper end has a similar pivot connection provided by a set screw assembly 61. Device 61 is received in an arcuate slot 62 formed in the outer end of a drive plate 63 furnishing the radially outward part of a bell-crank lever 64. Like device 57, set screw device 61 may be adjusted to and held at any desired position in the slot in which it is received by (l) loosening the set screw of the device, (2) sliding the device to the selected position, and (3) retightening the set screw of the device.

The radially inward end of the bell-crank lever 64 encircles and is fixedly secured to a rocker shaft (not shown) supported at opposite ends by balls received in sockets at the end of the shaft and in sockets provided by ball support plugs 70 received in bores 71 at opposite horizontal ends of a stand 72 mounted on base 54. The mentioned rocker shaft carries in fixed relation a drum sector means 75 comprised of a hub 76 secured to that shaft, an arcuate cylindrical rim 77 and radial webs 78 and 79 and side web 74 connecting the rim to the hub. The left-hand end (FIG. 2) of hub 76 is shaped to have an upwardly extending head 80 (FIG. 4) in the top of which is received a channel member 81 in which is received in turn an angular motion transmitting bar 82. Both the bar 82 and the channel member 81 are secured to head 80 by a screw 83. As shown (FIG. 2) most of bar 82 projects leftwardly of the drum sector means 75.

The entire described sector structure is adapted to be rocked about its rocker shaft by forward and back motions of the drive rod 60.

Disposed on the leftward side (FIG. 2) of the sector device 75 is a light projector 90 supported (FIG. 4) by a platform 91 mounted by a ball 92 on base 54 and adjustable in inclination with that base by a vernier screw assembly 93 of which the screw engages the forward end of the platform. Projector 90 emits a stationary scanning light beam in a path indicated by the dash line 94. The beam in that path is directed to a scanning head 95 separated from the front end of projector 90 by the gap 96.

As best shown in FIG. 2, the rim 77 of the sector structure 75 has a portion which extends leftwards of the side web 74 and is stiffened by triangular webs 97. The left-hand transverse margin 98 of that rim portion is disposed to the right of beam path 94 but is spaced from that path by only a small distance, i.e., a few hundredths of an inch. The outer face 100 of rim 77 is accurately machined to define with high precision a sector of a geometric circular cylindrical surface passing through gap 96 and having an axis coincident with that of the mentioned rocker shaft and normal to and intersecting the axis of the path 94 for the light beam from projection 90.

Rim face 100 serves as a template surface for a copy sheet in the form of a rectangular color transparency 105 providing the color image from which the color separation images are made by the described system. Sheet 105 is placed in contact with template surface 100 so that the opposite lateral edges 106 107 of the sheet coincide with generatrix lines of the geometric cylindrical surface defined by the template surface and so that, between those edges, the portion of the sheet over the template surface is bent or curved by the backing provided by that surface to conform very closely to the ideal cylindrical surface which is the desired shape for the copy sheet.

As shown in FIGS. 2 and 3, sheet is so positioned on template surface 100 that a leftward portion 110 of the sheet extends transversely into and across gap 96 to intercept the path 94 for the scanning light beam. Throughout the extent of portion 110, the sheet 105 is not backed by its template surface. Despite that lack of backing however, the stiffness of the sheet and the closeness to path 94 of the left-hand edge 98 of the template surface are factors which conjointly cause the unbacked portion of sheet 105 to have at its intersection with path 94 a negligible divergence from the described ideal geometric cylindrical surface.

Immediately adjacent the leftward transverse edge 98 of the template surface 100, sheet 105 is maintained in contact with that surface by a clamping means in the form of a resilient strap passing with tension from a zone of fastening 117 to surface 100 on one lateral side of sheet 105 to a zone of fastening 118 of the strap to the surface 100 on the other lateral side of the copy sheet. In extending between those two zones of fastening, strap 115 pass circumferentially over the sheet 105.

Strap 115 may be provided by, for example, a resilient strip of tape having an underside coated with adhesive at the fastened ends of the strip but non-coated with adhesive over the strip portion in contact with the copy sheet. Because the strap 115 is tensioned between its end zones at which it is fastened to the template, the strap presses the portion underneath of sheet 105 into firm contact with the template surface 100. On the other hand, because the copy sheet and strap are not fastened together, the sheet may be moved transversely beneath the strap by a force overcoming the friction between the sheet and strap.

To the end of imparting such transverse movement to the copy sheet 105, the left-hand transverse margin 119 of the sheet is gripped between the arcuate rim 120 of a drum sector means 121 and an arcuate clamping bar 122 (FIG. 5) drawn to the rim 120 by screws 123 passing through that bar and through the copy margin 119 to be received in threaded holes in the rim 120. As shown, the sector device 121 is on the opposite side of beam path 94 from sector device 75 and is generally similar to the latter in that'the rim of device 121 is connected by radial webs 124, 125, and a side web 126 to a hub 127 mounted on a rocker shaft (not shown) coaxial with the rocker shaft for sector device 75. As a further similarity, the outer face 128 of the rim of sector device 121 conforms to the geometric circular cylindrical surface defined by the template surface 100 on the sector device 75. A difference between two sector devices is that whereas device 75 is mounted on a transversely stationary stand 72, device 121 is mounted on a carriage 130 (FIG. 5) transversely movable on ways 131 and 132 in a direction normal to the axis of beam path 94. Another difference is that, whereas the angular motion transmitting bar 82 (FIG. 2) is fixed to sector device 75, bar 82 is transversely slidable within the channel member 133 of sector device 121, in which bar 82 is received.

The carriage 130 for sector device 121 is moved transversely by a sine bar linkage 135 coupling that carriage to carriage 25 for the glow lamp projectors. Such linkage is comprised in part (FIG. 1) of a strut projecting from the side of carriage 25 and of a long bar 141 pivotally connected at one end to strut 140 and pivotally connected at the other end to the radially outer end of a ratio bar 142. Bar 142 at its radially inner end is angularly movable about a pivot 143 fixedly connected to the bed 10. The central portion of bar 142 has formed therein a lengthwise extending arcuate slot 144 within which is received a set screw assembly 145. That assembly provides a pivotal connection for the right-hand end of a short bar 146 of which the left-hand end is pivotally connected to a strut 147 projecting outwardly from the carriage 130. Set screw device 145 can be adjusted to and maintained at any desired position along slot 144 by loosening the set screw of the device, sliding the device to the selected position, and then retightening the screw of the device.

In a sine bar linkage of the sort described, the ratio of the respective linear movements of bars 141 and 146 is approximately equal to the ratio of the distances from pivot 143 of the respective pivotal connections of bars 141 and 146 to the ratio bar 142. It follows that selective adjustment of the set screw assembly 145 in slot 144 effects selective adjustment in the ratio of the linear movements of the bars 141 and 146.

To complete the description of the mechanical details of the FIG. 1 embodiment, the auxiliary cam 48 operates a microswitch 150 to selectively change the electrical condition of that switch between open and closed conditions A cable 151 connects switch 150 in circuit with the skip-scan circuits 35 to provide for control of that unit by the switch actron.

OPERATION The setting up and operation of the described system are as follow:

Assume that the colored image to be reproduced from a copy sheet 105 has a size x in the circumferential direction of template surface 100 and a size y in the transverse direction of that surface. Those circumferential and transverse directions correspond to, respectively, the circumferential x and axial y directions over the surface of drum 12 on which the film sheets 17-20 are mounted. Assume that the color separation images to be exposed on those film sheets are to be the same in shape as but larger in size than the original color image on copy sheet 105. Such congruence between the color separation images and the original colored image is realized by satisfying the relations:

aV V, 1

r (2) where a is the enlargement ration, V is the linear velocity in the direction x of the scanning beam from projector 90 over copy sheet 105, V, is the linear velocity in the direction of x of the exposing beams over the film sheets 17-20 D, is the size in the direction y of each step of transverse movement of sheet 105, and D,,- is the size in direction y of each step of axial relative movement between drum 12 and the exposing light beams from the glow lamp projectors,

Relation (l) is satisfied by adjusting set screw device 57 (FIG. 4) to a position within slot 51 at which, during the first of two consecutive revolutions of drum 12 (FIG. 1), the rod 60 rocks sector means 75 upwardly at an angular speed causing the linear scanning speed of beam 95 over copy sheet 105 to be l/a of the linear scanning speed of the exposing beams over the drum l2. Concomitant with the adjustment just described, set screw device 61 is positionally adjusted within slot 62 and film sheets 1720 are positioned on the circumference of drum 12 such that the interval during which beam 94 will scan the color image on sheet 105 will be coincident in time with the interval during which the exposing beams will scan over the film sheets.

Relation (2) is satisfied by adjusting the position of set screw device 145 within slot 144 to cause a unit transverse movement of carriage 25 'to be converted by the sine bar linkage into a transverse movement of l/a of the carriage 130.

With both relations (I) and (2) satisfied as discussed, the raster scanning pattern developed by beam 94 over the copy sheet 105 will be duplicated in the same shape but in larger size by the raster scanning pattern with which the exposing light beams scan over the film sheets. The enlargement ratio a is, of course, selectively variable by means of the mentioned adjustments. Having set up the equipment as described, carriages 25 an 130 are positioned, so that the paths for the exposing beams intercept the right hand end portions (FIG. 1) of the film sheet's 17-20, and the path 94 for the scanning beam inter- One complete effective line scanning of that image occurs during each non-overlapping pair of consecutive revolutions of drum 12. During the first revolution in each such pair, cam 41 (which rotates at half the speed of drum 12) drives linkage 49, 50, 51, 55, 60, 63 to rock the sector device 75 upward through a predetermined angle from a reference angular position for the device. Such movement of device 75 is transmitted through bar 82 to sector device 121 to cause the latter device to rock upward by the same amount.

The upward rocking motions of devices 75 and 121 causes the beam in path 94 to scan in a line down over the image on the copy sheet 105. As the beam so scans and passes through the copy sheet, the beam is modulated in color and in intensity by the scanned tone values of the original image. Thereafter, the beam is received by head 95 which (in a well known manner) converts the color and intensity modulation of the beam into blue, green and red color component signals supplied via cable 42 to the unit 41. That processing unit derives from those input signals the yellow, magenta, cyan and black signals supplied by way of skip-scan control unit 35 to, respectively, the projectors 27, 28, 29 and 30. The last-named signals control the current through the glow lamps of the projectors so as to modulate the intensity of the light beams therefrom. As the result of, conjointly, that modulation and the rotation of the film sheets beneath the beams to produce a line scan of each beam over the corresponding sheet, each beam exposes on its associated sheet a line of detail drived from the concurrent line scanning of the copy sheet 105 and forming part of the separation image exposed by that beam on such film sheet.

As stated, the foregoing actions occur during the first revolution in each non-overlapping pair of consecutive revolutions of drum 12. During the second revolution in each such pair of revolutions, cam 47 and the cam-driven linkage serve to rock the sector devices 75 and 121 downwardly back to reference angular positioned. In the course of that return movement of the sector devices, the beam 94 moves over a portion of copy sheet 105 which has already been scanned. Hence, if the copy sheet were to be effectively scanned during such return movement, spurious information would be exposed on the film sheets 17-20 by the beams from projectors 27-30. To prevent such information from being so recorded,

cam 48 operates during the mentioned second revolution of drum 12 to actuate microswitch l50 to effect through unit 35 an extinction of the glow lamps 26 in the projectors 27-30 and a consequent blanking of the exposing beams from the projectors.

Thus, the FIG. 1 embodiment has a skip-scan action providing the principal advantage that the film sheets 17-20 may be wrapped around drum 12 to occupy all or most of the full circumference of the drum. Absent that skip-scan action, the exposing of spurious information on the film sheets during the return stroke of the sector devices 75 and 121 could be avoided only by having such stroke occur during the period when the exposing beams are falling on a blank area of the drum between the opposite edges of the film sheets wrapped on the drum. In order, however, to make that period long enough for the full return stroke of devices 75 and 121 to occur within such period, it would be necessary to limit the wrap of the film sheets around the drum to less than half the drums circumference.

Another event occurring in the second revolution of each of the mentioned pairs of revolutions of drum 12 is that an indexing takes place of the carriages 25 and 130. Specifically, during the second revolution, indexing device 31 moves carriage 25 one incremental axial step to the left to thereby position the beams from the glow lamp projectors to scan a new line over the film sheets. The step movement of carriage 25 is converted by the described sine bar linkage into a lesser transverse step of leftward movement of carriage and of the sector device 121 (FIG. 2) mounted on that carriage. Although section device 121 is locked by bar 82 to the transversely stationery device 75 in respect to angular motion, the leftward stepwise movement of device 121 relative to device 75 is permitted by the sliding of bar 82 in its seat in the moving sector device.

Since the lefthand margin of copy sheet 105 is gripped by the sector device 121, the leftward indexing by a step of that device produces a leftward pulling of one incremental step of the copy sheet 105 so as to position that sheet for a new line of scanning by the beam in path 94. The cylindrically curved copy sheet undergoes that stepwise movement by sliding over the template surface 100 of the transversely stationery device 75 and by slipping beneath the strap 115 which resiliently presses the copy sheet against such surface. In this manner, the copy sheet in the course of a scanning cycle is progressively pulled leftward until most of the sheet is to the left of surface 100 so as to receive no backing from that surface. Even so, because sheet 105 is somewhat stiff and the lefthand edge 99 of surface 100 is very close to the path 94 for the scanning beam and because, further, the portion of sheet 105 still resting on surface 100 is pressed in the vicinity of edge 98 against that surface by the clamping strap 115, the portion of sheet 105 intercepted by the scanning beam path 94 continues to conform with negligible distortion to the geometric cylindrical surface representing the ideal shape for the bent copy sheet. The FIG. 1 system makes possible, therefore, the acceptable reproduction of colored original images which are much larger than those which could be reproduced by the scanning mechanism disclosed in the aforementioned U.S. Pat. No. 3,109,888.

At the end of the second in the considered pair of revolutions of drum l2, cam 48 actuates microswitch 150 to operate through unit 35 to re-start the glow lamps 26 of the projectors 27-30. During the next and succeeding pairs of revolutions in the scanning cycle, the FIG. 1 system repeats the operations already described.

SKIP-SCAN CIRCUIT Unit 35 is comprised of duplicate circuits of which there is a respective one for each of the projectors 17-20, and of which all are controlled in parallel by the microswitch 150. The circuit forthe glow lamp 26 of projector 27 is shown schematically in FIG. 7.

In that Figure, the glow lamp is connected by leads 160 and 161 between a source of +180 volts d.c. and ground. The cathode of the glow lamp is in series with a diode D in turn in series with two parallel circuit branches consisting of, respectively, the collector-emitter path of transistor Q and resistor 162 in series and the collector-emitter path of transistor Q and resistor R in series. The image signal on lead 37 is applied to the base of transistor Q by way of a gate circuit 163 which passes or blocks the image signal in response to a control signal applied to circuit 163 by lead 164 from the movable contact 165 of microswitch 150. The same control signal is fed by lead 166 and resistor 167 to the base of transistor Q to control the conductivity of that transistor.

Another circuit between the source of 180 volts do and ground is comprised of the connection in series of (a) the primary 170 of a voltage multiplying pulse transformer 171, (b) a charge-storing capacitor 172, and (c) the collector-emitter path of a transistor 0,. The secondary winding 173 of transformer 171 is connected to the anode and cathode leads 160, 161 for glow lamp 26 by, respectively, a resistor R and a diode D,,, the forward direction of conduction of the latter being away from the cathode of the glow lamp. A diode D, is connected as shown across the primary winding 170 of the transformer. Capacitor 172 is shunted by a discharge resistor R,. The base of transistor 0, is connected by a resistor 174 to the movable contact 165 of the microswitch 150.

During the first of each two non-overlapping consecutive revolutions of drum l2, movable contact 165 is positioned by auxiliary cam 48 to be closed with a fixed contact 180 connected to a supply of +10 volts d.c. During the second revolution in that pair of revolutions, the combined actions of cam 48 and of a biasing spring 181 move the contact 165 to closed position with a fixed contact 183 connected to a supply of 0.5 volts d.c.

The operation of the FIG. 7 circuit is as follows.

As stated, both the copy sheet and the film sheets are lined scanned during the first out of every two revolutions of drum 12. In the course of that scanning, movable contact is closed with fixed contact 180 to supply +10 volts dc. to gate 163 to permit the image signals to pass to transistor 0, so as to produce a variation in the conductivity of that transistor and a corresponding variation in the amount of current drawn through glow lamp 26. Simultaneously, the +10 volts signal is supplied to transistor 0, to render that element high in conductance. The purpose in so making Q: in effect a closed switch" is that, if the image signal to Q transiently drops to value so low that 0,, would be alone unable to maintain glow lamp 26 fired, such glow lamp will still remain on" because of current drawn through it by the supplementary path comprised of keepalive resistor R and transistor 0,.

During the second of the mentioned two revolutions of drum l2, movable contact 165 closed with fixed contact 183 to thereby apply -O.5 volts to gate 163 and transistor 0 to thereby extinguish glow lamp 26 and the light beam from that glow lamp.

Upon completion of that second revolution, and the starting of the first revolution in the next pair thereof, movable contact 165 shifts from closure with contact 183 back to closure with contact 180 so as to re-establish the condition necessary to keep glow lamp 26 fired once it has been re-started. Without anything more, however, the time at which glow lamp 26 would fire would be uncertain because it would depend upon a random event such as receipt by the gas in the glow lamp of sufficient ionizing radiation in the form, say, of a cosmic ray or other high energy particles. Such uncertainty as to the time of firing is, however, avoided in the FIG. 7 circuit as the result of the change in position of contact 165 from closure with contact 183 to closure with contact 180.

Specifically, when the movable contact shifts back to closure with fixed contact 180, the +10 volts signal is supplied to transistor Q, to change the condustance of that transistor from low to high. The increased conductance 'of transistor Q, causes a transient pulse of current to fiow through the primary winding of transformer 171 and into capacitor 172 to charge that capacitor. When transformer 17] is so pulsed, it develops at the output of its secondary 173 a transient high voltage which drives the cathode of glow lamp 26 down in voltage to a value at which the ensuing cathode-anode voltage of the glow lamp produces a firing of that lamp. At its peak, the described transient voltage may produce across the glow lamp a cathode-anode voltage on the order of 300 or more volts. Once the glow lamp has thus been fired, it remains fired because the transistor Q, and Q at that time have been rerendered of high enough conductance to establish circuit operating conditions effective to produce a discharge-maintaining potential across the glow lamp.

During the described re-starting of the glow lamp 26, resistor R prevents excessive current from being drawn through the glow lamp in the circuit including the glow lamp itself and transformer secondary 173. Diode D concurrently prevents transistor Q, from being reversed biased. Diode D, has no function during the re-starting period but serves during normal operation to prevent excessive current from being shunted around the glow lamp through the secondary winding 173.

The current pulse through transformer primary 170 and the corresponding voltage pulse across the glow lamp are terminated by the full charging of capacitor 172. Thereafter, a trickle of steady state current is drawn through primary winding 170, resistor R, and transistor Q, so long as movable contact 165 is closed with fixed contact 180. When the movable contact subsequently shifts to open with contact and close with contact 183, the current through primary winding 170 the reverse kick from the transformer which would otherwise be produced by that decrease in current. When transistor O is opened" as described by the shifting of movable contact 165, capacitor 172 discharges through resistor R so as to be ready to generate the next re-starting pulse.

The FIG. 7 circuit thus serves to reliably re-start with accurate timing an extinguished glow lamp. While the circuit has been described in connection with the skipscan technique of scanning copy, the circuit is not limited to that particular application but has other applications as well. For example, such circuit is also very useful where the image signals derived from the scanning of a copy sheet are replaced for a portion of the scanning of that sheet by fixed signals which produce solid color printing in the final reproduction, and which are selected by a knock-out mask as described in co-pending U.S. application Ser. No. 649,621 filed June 28, 1967 in the name of Bartel et al., and owned by the assignee hereof. For that knock'out mask application, microswitch 150 is replaced by a blanking trigger signal derived from the knock-out mask, gate 163 is eliminated, and means are provided to selectively control the conductance of transistor Q either by the image signal from the scanned copy sheet or by a fixed value signal selected by the mask.

The above-described embodiments being exemplary only, it is to be understood that additions thereto, modifications thereof and omissions therefrom can be made without departing from the spirit of the invention, and that the invention comprehends embodiments differing in form and/or detail from that which has been specifically disclosed. For example, the described apparatus may be modified to omit the skipscanning feature, the modifications involved being to employ: (a) a gear box with a 1:] transmission ratio, (b) a carriage drive 31 producing one axial stepwise movement of carriage 25 and 130 for each revolution of drum 16, (c) film sheets 17-20 of small enough size so that the wrap of each around drum 16 is less than half the drum circumference, the film sheets being angularly positioned on the drum so that the beams from glow lamps 27-30 scan a blank area of the drum during the return rocking stroke of the copy sheet 105.

As another example, while it has been disclosed as a feature of skip-scanning that carriages 25 and 130 are indexed axially by one step during the second one of each non-overlapping pair of consecutive revolutions of drum 16, the indexing need not take place during such second revolution. On the contrary, since the size of the stepwise indexing movement is very small compared to the size of the distance swept out in each line scan of the copy sheet and film sheets, the indexing step may occur at any time within the time period of a corresponding pair of drum revolutions without having any noticeable effect in the color separations produced on the film sheets. That is, so long as one indexing step is produced for each pair of consecutive non-overlapping revolutions of drum l6, and the delay between the start of each such indexing step and the start of the corresponding pair of revolutions is maintained constant throughout any one scanning cycle, the amount of such delay is not critical and may be adjusted as desired. Hence, it is entirely feasible for the indexing step to occur during the first rather than the second of the pair of corresponding drum revolutions.

Accordingly, the invention is not to be considered as limited save as is consonant with the recitals of the following claims.

We claim:

1. In a system in which a glow lamp emits a light beam which is controlled by signal regulating the current through said lamp and which scans over a sensitized photographic film sheet to expose on said sheet an image derived from said signal, the improvement comprising, first transistor means responsive to said signal to regulate the current through said lamp and thereby control the intensity of said beam, switch means to interrupt the current through said glow lamp for a controlled period to thereby blank said beam for that period, and circuit means including second transistor means responsive to termination of said period to maintain an alternative conducting path for the current through said lamp to thereby insure current flow said lamp and third transistor means responsive to termination of said period to re-start said glow lamp by applying across said lamp a transient voltage which substantially exceeds the normal starting voltage of said lamp and which fires said lamp.

2. The improvement as in claim 1 in which said switch means comprises means to interrupt the application of said signal to said first transistor means.

3. The improvement as in claim 1 in which said circuit means comprises a voltage multiplying transformer having its output coupled across said lamp and its input coupled to a power supply through the series connection of current-absorbing capacitor means and said second transistor means, the latter means being responsive to said termination of said period to change from a high to a low impedance in said series connection, and said circuit means further including means to discharge said capacitor means in between the occurrence of such period and the next such period.

4. The improvement as in claim 1 in which said film sheet is mounted on a drum which rotates and partakes of axial movement relative to said beam to produce scanning in two orthogonal directions of said beam over said sheet, in which a copy sheet is mounted on an arcuate sector that rocks forward during one rotation of said drum and backward during the next rotation, and in which said switch means comprises means response to rotation of said drum to interrupt said glow lamp circuit during the backward rocking movement of said sector to allow enlargement of said film sheet to the extent of the circumference of said drum.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,678,187 Dated July 18, 1972 lnventofls) Byron L. Barkman, William West Moe and Austin Ross It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col 1 line M, "to" should read --at---; Col. 3 line 6 "projection" should read "projector-; Col. 6 line 36, "positioned" should read -'-position--; C 1, 8 li 1LT, after "t second occurrence, insert a Col. 10 line 23, after "flow" insert -through--.

Signed and sealed/this 6th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents mg? UNITED STATES PATENT orrrcr v CERTIFICATE OF EQTE Patent No. 3, 7 ,1 7 Dated July 18, 1972 I Byron L. Barkman, William West Moe and Austin Ross It is certified that error appears in the above-identified patent and that said Letters Patent are hereby -corrected as shown below:

Col, 1 line ML, "to" should read --a.t--; Col. 3 line 6 "projection" should read --projector--; Col. 6 line 36, "positioned" should read -position--; l, 8 li 1A, aft r "t second occurrence, insert a C01. 10 line 23, after "flow" insert --through--.

Signed and sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. In a system in which a glow lamp emits a light beam which is controlled by signal regulating the current through said lamp and which scans over a sensitized photographic film sheet to expose on said sheet an image derived from said signal, the improvement comprising, first transistor means responsive to said signal to regulate the current through said lamp and thereby control the intensIty of said beam, switch means to interrupt the current through said glow lamp for a controlled period to thereby blank said beam for that period, and circuit means including second transistor means responsive to termination of said period to maintain an alternative conducting path for the current through said lamp to thereby insure current flow said lamp and third transistor means responsive to termination of said period to restart said glow lamp by applying across said lamp a transient voltage which substantially exceeds the normal starting voltage of said lamp and which fires said lamp.
 2. The improvement as in claim 1 in which said switch means comprises means to interrupt the application of said signal to said first transistor means.
 3. The improvement as in claim 1 in which said circuit means comprises a voltage multiplying transformer having its output coupled across said lamp and its input coupled to a power supply through the series connection of current-absorbing capacitor means and said second transistor means, the latter means being responsive to said termination of said period to change from a high to a low impedance in said series connection, and said circuit means further including means to discharge said capacitor means in between the occurrence of such period and the next such period.
 4. The improvement as in claim 1 in which said film sheet is mounted on a drum which rotates and partakes of axial movement relative to said beam to produce scanning in two orthogonal directions of said beam over said sheet, in which a copy sheet is mounted on an arcuate sector that rocks forward during one rotation of said drum and backward during the next rotation, and in which said switch means comprises means response to rotation of said drum to interrupt said glow lamp circuit during the backward rocking movement of said sector to allow enlargement of said film sheet to the extent of the circumference of said drum. 